The present invention relates to a method and apparatus for imprinting an indelible ink image upon a selected substrate. Such indelible inked images are particularly desirable for use in imprinting any informational images, such as a scanable bar code, upon selected substrates that are exposed to unusually harsh environments as in industrial applications. Although the following discussion uses scanable bar codes as an example of the particular usefulness of the present invention, it is to be understood that the method and apparatus taught herein may be used on any suitable substrate and for the imprinting of other useful indicia such a sequential numbering, operating data, warning notices, etc. where long life legibility of the imprinted material is required.
Many devices exist for reading bar codes printed on packages and other objects. Bar codes may be printed on retail merchandise for product and price identification at the point of sale, warehouse inventory control, process control, and many other applications.
The basic principle employed in bar code reading devices is the detection of contrasting reflected light. A source of illumination such as a low a powered helium neon laser, produces a beam of light which is may be moved across the bar code imprint. Dark areas (bars) absorb laser light, whereas light areas (spaces) reflect light that is detected by a scanner.
Optics are typically used to expand the laser beam into a line of laser light and to move the expanded laser beam across the area containing the bar code. Without the use of optics, the laser beam would only appear as a point of light. This process is commonly referred to as “moving-beam scanning.” As the moving beam travels across the area to be scanned for a code, commonly called the scanning zone, the light and dark transition areas are detected and converted to a digital signal known as the code. A typical bar code consists of a defined number of light and dark transition areas having given ratios between the wide and narrow intervals.
Thus a scanable bar code consists of a series of solid parallel bars separated by open spaces. The bars and spaces are printed at either a full width or half width. The bars and spaces signify a bit pattern wherein wide spaces or bars are assigned a “one” while narrow spaces and bars are assigned a “zero” (or vice versa).
Prior art U.S. Pat. No. 3,728,677 employs a mirrored wheel having a polygonal periphery. Rotation of the mirrored wheel scans a laser beam across two azimuthally spaced mirrors, which deflect the beam downwardly to trace an “X” shaped pattern.
It is also known to use prisms and mirrors, or other apparatus, to turn the scanning beam direction of an optical code scanning system. For example see U.S. Pat. Nos. 3,663,800; 3,774,014; 3,800,282; 3,902,047; and 4,064,390.
U.S. Pat. No. 3,906,203 teaches scanning a bar code and measuring its interval widths by recording the time required to traverse each interval. The successive interval widths are then multiplied by a constant such as three, five, or eight. By storing and comparing the multiplied widths of successive scans, the scanner can determine whether the latest interval is about the same size as, or much smaller, or larger, than, the prior interval.
From the above description of bar codes, their formats and how they function, it is understandable that for a bar code system to function accurately it is desirable that the bar code, printed upon the object being scanned, contain clear undistorted set of dark and light parallel lines or bars. However, in many industrial applications and uses, the imprinted bar codes may be damaged by abrasion, chemicals, solvents and/or heat to the extent that the bar code or portions thereof maybe obliterated or otherwise unreadable.
Accordingly there is a need for a method and apparatus for imprinting a durable bar code that will resist the harsh environment of the industrial workplace.